Elk Grove has been a powerhouse of medical activity. All four health systems in Greater Sacramento have a presence there, and many are considering growing. Just last week, Kaiser Permanente officials confirmed plans to buy 7.5 acres for a second medical office building. The land is adjacent to the proposed Elk Grove Promenade mall, west of Highway 99. The health care giant dominates the market. More than half the people with health insurance who live in the area are members. But the other groups aren’t getting shut out. Sutter Health and Catholic Healthcare West are considering adding more office buildings and two hospitals. And the UC Davis Health System, which already has one building in the city, is watching growth. Currently, Elk Grove has six medical buildings and no hospital.